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My Pentax K-5 comes with a "regular" low ISO setting of 100, but if you enable "expanded ISO" you can set it as low as 80 (plus go up to an absurd 51200!). I know that in general to reduce noise, lower ISO settings are better, but I'm wondering if that holds true for this "expanded" setting as well. If I'm outside and there's plenty of light and I can use 80 ISO without ruining my shot with inappropriate shutter and aperture settings, should I?

(I know there may be certain specific circumstances where the super-low ISO would be helpful, e.g. if you are shooting right into the sun and don't want the shutter at 1/8000 s. That's not the situation I'm talking about.)

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True, lower ISO does typically bring lower noise, but all digital cameras adjust ISO by altering internal exposure sensitivity, and any change from the 'native' ISO typically introduces some noise, or other trade-off, such as dynamic range. This includes setting ISO below the 'native' ISO.

This 'native' ISO is that for which the sensor and electronics are optimized. Other ISOs are achieved by pushing (or pulling) exposure internally.

Since your camera offers this 'expanded ISO" that provides for 80 ISO, you can assume that this ISO is sub-optimal, and could exhibit more noise or a loss of dynamic range than the 'native' ISO. Unfortunately, few camera manufactures publish what the 'native" ISO is, but for the most part it is assumed to be the lowest ISO in normal settings. Some suggest Canon cameras are 'native' for ISO 100, and full stop ISO are best (100,200,400 etc.), but I haven't seen such results for Pentax.

Google for "native ISO" and you likely will find some interesting discussion and even sample images.

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  • \$\begingroup\$ I think you want that to be 100, 200, 400 for "full stop ISO". \$\endgroup\$
    – jrista
    Apr 27, 2011 at 5:19
  • \$\begingroup\$ Yes, @jrista, you are right, and thanks, not sure how "300" slipped in there...correcting "100,200,300" to "100,200,400" \$\endgroup\$
    – cmason
    Apr 27, 2011 at 11:32
  • \$\begingroup\$ I'm not sure you can just assume the K5's native ISO is above 80, Canon's expanded low ISO is 50, presumably to keep in in the whole stop sequence, but I'd bet that 80 is actually the native ISO of the k-5, otherwise it's an odd value to choose. \$\endgroup\$
    – Matt Grum
    Apr 27, 2011 at 12:14
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    \$\begingroup\$ If the Pentax native ISO is 80, then why would one need to activate a custom function to enable it? If native, it should be, well, native and one of the available ISOs from the menu. My supposition, and it is a supposition, is just this: the Pentax likely does not have 80 as its native ISO because it needs a special function enabled for it to be active. I am not speaking to what ISO the camera actually exhibits when it is set for ISO 100, only what must be done in the camera settings to enable ISO 80. \$\endgroup\$
    – cmason
    Apr 27, 2011 at 13:17
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    \$\begingroup\$ The Pentak K5 does indeed have a native ISO range of 100-12800. The ISO 80 setting is not native, hence its categorization of expanded ISO. @cmason is correct in his assertions. Many cameras seem to choose an expanded low ISO of 80 rather than 50 since their "true base" ISO is 160 rather than 100. \$\endgroup\$
    – jrista
    Apr 27, 2011 at 17:36
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You can use it and it gives excellent dynamic-range and very low image noise but really barely any different from the ISO 100 setting.

What helps more is the use the Dynamic Range Expansion function. This will limit the ISO sensitivity to 200-12800 normally or 160 to 51200 with Expanded ISO turned on. You get extremely low noise but an extra stop of dynamic-range for highlights.

The ISOs above 12800 are of no use to me due to their performance and I do not want to accidentally use them, I keep the expanded ISO off and the expanded range on. This gives me ISO 200 is my base setting.

To use slower shutter-speeds in bright light, rather than reducing the ISO, use an ND filter.

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    \$\begingroup\$ Hah, I didn't know you were a Pentax shooter. There's a surprisingly large number of us on this site. \$\endgroup\$
    – Joanne C
    Apr 27, 2011 at 2:56
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    \$\begingroup\$ Pentaxians are known to be the research-oriented type. How else would they have ended up with a Pentax? \$\endgroup\$
    – eruditass
    Apr 27, 2011 at 7:27
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    \$\begingroup\$ Pentax DSLRs are my tools of choice for travel photography since I consider them the most efficient cameras to use. I own 2 Pentax and also 6 cameras from 3 other brands, so I'm not exclusive ;) I match tools to assignment, plus I take advantage of other cameras which regularly pass through my hands. \$\endgroup\$
    – Itai
    Apr 27, 2011 at 13:53
  • \$\begingroup\$ Thanks for the tip about Dynamic Range Expansion, I had ignored that setting. \$\endgroup\$
    – Hank
    Apr 27, 2011 at 14:00
  • \$\begingroup\$ Does Dynamic Range Expansion work on RAW files or is it purely a JPEG feature? \$\endgroup\$
    – CadentOrange
    Jun 28, 2011 at 12:01
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With JPEG, you will not notice any difference. If you shoot JPEG with the K-5, definitely turn on highlight correction which will shift the DR from the shadows (lost in JPEG) to the highlights, but you'll still notice little difference from highlight corrected ISO 160 to 200.

If you shoot RAW, you will get around a 0.4 stops of increased dynamic range (less noise in the shadows) if you decide to heavily dodge your shadows. This is because the native ISO of the K-5 isn't 100, it's somewhere less than 100. Pretty much all cameras don't have a native ISO of exactly 100, but subscribe to the current 'standard ISOs" of 100, 200, 400, etc. For those with a native ISO above 100, what you'll get is a reduction of dynamic range, but this is not the case with the K-5.

The DR is pretty huge on that sensor and it'd be hard to notice anyway. A bigger benefit to ISO 80 is that you can lower the shutter speed or wider aperture if you need to.

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Speaking as someone with a couple of k-5s, I can't say that I've ever noticed any real difference in the image quality at ISO 80 versus ISO 100. While there's probably some difference in the outcome to the lesser when it comes to the expanded range, it is so minute that I can't really detect it. Now, on the other end, that's a different story, ISO 51200 is pretty close to unusable though it may be the only way you get anything, so that's something at least. At best, though, you're printing 4x6 and hoping it's sort of decent. :)

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"Since your camera offers this 'expanded ISO" that provides for 80 ISO, you can assume that this ISO is sub-optimal"

Actually with the general new generation of cameras the exact opposite is true. Most are able to keep their dynamic range fairly well and what actually happens is that the camera generally shoots an exposure a stop brighter than what is assumed, and then as it goes through the Gamma Curve to be a viewable Raw file, that extra stop (about double the data for your shadows through midtones) gets driven down into your shadows and midtones for more real information and a massive reduction of noise or extrapolation/interpolation. Meaning, REAL detail. With real detail, an image can handle a lot more Raw Deconvolution sharpening (radius to the left detail to the right in Lightroom or Camera Raw) because there is no artifacting where the noise would have been eliminated (a graininess) by a color noise algorithm. Most of these files need little to NO color noise reduction at all. The Raw Deconvolution Capture sharpen then allows for upwards to 10% more quality to an enlargement. This is very significant. If dynamic Range is tough to shoot, and may be in question then maybe try both Iso Expansion Low and Native ISO, just to be safe.

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